Chemiluminescence and kinetic studies in O(3P)+ thiophene, pyrrole and furan mixtures

Abstract

Using fast-flow-discharge apparatus the reactions between oxygen atoms and thiophene, pyrrole and furan have been studied. Chemiluminescence has been observed from the electronically excited states of SO2 and CH in thiophene + O(3P); NO, CH, CN and NO2 in pyrrole + O(3P) and OH in furan + O(3P), and the evolution of its intensity has been monitored as a function of reactant concentration. Kinetic determinations have been done for the reaction of O(3P) and thiophene by following the SO*2 emission intensity and the O(3P) decay, using the titration of residual oxygen atoms with NO, at several temperatures, and for the reaction of O(3P) and pyrrole at 318 K by following the decay of O(3P) with NO. For the thiophene reaction, rate constants in the range T= 379–525 K can be fitted to the Arrhenius expression k=(1.6 ± 0.2)× 1012 exp (–240 ±/RT) cm3 mol–1 s–1 and for the pyrrole reaction the value of the rate constant at 318 K is k=(2.8 ± 0.3)× 1012 cm3 mol–1 s–1. Different reaction mechanisms are proposed in the light of the observed emissions and the empirical correlation existing between the kinetic parameters and the ionization potential of the aromatic hydrocarbons. A comparison is made with the reactions of O(3P) and benzene and O(3P) and pyridine.